The present invention relates to a device for adjusting the transverse position of a strip of packaging material on a machine for packaging pourable food products.
Machines for packaging pourable food products, such as fruit juice, wine, tomato sauce, pasteurized or long-storage (UHT) milk, etc., are known, in which the packages are formed from a continuous tube of packaging material defined by a longitudinally sealed strip.
The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal material, e.g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product.
To produce aseptic packages, the strip of packaging material is unwound off a reel and fed through an aseptic chamber, in which it is sterilized, for example, by applying a sterilizing agent, such as hydrogen peroxide, which is later evaporated by heating, and/or by subjecting the packaging material to radiation of an appropriate wavelength and intensity, and the sterilized strip is folded into a cylinder and sealed longitudinally to form, in known manner, a continuous vertical longitudinally sealed tube. In other words, the tube of packaging material forms an extension of the aseptic chamber, and is filled continuously with the pourable food product and then sent to a forming and (transverse) sealing unit for forming the individual packages and in which the tube is gripped between pairs of jaws to seal the tube transversely and form pillow packs, which are then separated by cutting the sealed portions between the packs.
The pillow packs are then fed to a final folding station where they are folded mechanically into the finished shape.
On known packaging machines of the type briefly described above, the strip of packaging material, before being folded into a tube, is fed along a path defined by pairs of cylindrical, powered or idle rollers extending across the full width of the strip, but which do not guide the strip transversely.
The transverse position of the strip is defined by manually adjusted guide devices comprising a pair of rollers cooperating on opposite sides with a longitudinal portion, close to the edge, of the strip, and carried by a slide movable along a guide in a direction parallel to the strip feed plane and perpendicular to the strip feed direction.
Any error in the transverse position of the stripxe2x80x94which may occur, for example, after splicing two reels or in the event the strip deviates laterally as opposed to being perfectly straightxe2x80x94may result in faulty packages.
When a fault is detected, e.g. by inspecting the packages coming off the machine, the error is correctable by manually adjusting the guide device. The time taken, however, to stop the machine, make the manual adjustment and restart the machine results in a considerable loss in production, both in terms of downtime and the packages rejected.
It is an object of the present invention to provide a device for adjusting the transverse position of the strip of packaging material, designed to eliminate the aforementioned drawbacks typically associated with known devices.
According to the present invention, there is provided a device for adjusting the transverse position of a strip of packaging material on a packaging machine for producing packages containing a pourable food product, the device comprising:
a slide movable in a first direction parallel to a feed plane of said strip and substantially perpendicular to a feed direction of said strip in said plane;
gripping means carried by said slide and for gripping in sliding manner an edge of said strip; and
adjusting means for adjusting the position of said slide in said first direction;
characterized in that said adjusting means comprise an actuator for controlling said slide; a first sensor for detecting a first limit position of said strip and generating a first signal; a second sensor for detecting a second limit position of said strip and generating a second signal; and a control unit connected to said first and said second sensor, and which controls said actuator to move said slide towards said second limit position of said strip in response to a value of said first signal indicating said first limit position of said strip has been exceeded, and towards said first limit position of said strip in response to a value of said second signal indicating said second limit position of said strip has been exceeded.